Electronic apparatus

ABSTRACT

According to one embodiment, an electronic apparatus includes a receiver and a transmitter. The receiver is configured to receive, from a first wireless apparatus, a first physical frame including a destination address receivable by a second wireless apparatus different from the electronic apparatus. The transmitter is configured to transmit, to the first wireless apparatus, a first response frame including first information regarding the first physical frame, if the first physical frame is successfully received. A transmission period of the first response frame at least partially overlaps with a transmission period of a second response frame including second information regarding the first physical frame received by the second wireless apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority fromJapanese Patent Application No. 2018-161575, filed Aug. 30, 2018, theentire contents of which are incorporated herein by reference.

FIELD

Embodiments described herein relate generally to an electronicapparatus.

BACKGROUND

In recent years, various techniques for improving reliability ofcommunication have been proposed. One of those techniques is to transmitone piece of data to a plurality of wireless base stationssimultaneously using one wireless terminal. With this technique, thewireless terminal can refer to responses from the plurality of wirelessbase stations, whereby the reliability of communication can be improved.

However, with the technique described above, the wireless terminalsequentially refers to responses from the plurality of wireless basestations in a time-sharing manner, whereby there is a disadvantage thatthe overhead may be increased. Accordingly, there has been a demand fora new technique by which such inconvenience can be overcome.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an exemplary wireless communication environmentaccording to one embodiment.

FIG. 2 illustrates an exemplary frame format of a media access control(MAC) frame used in a wireless communication environment according tothe embodiment.

FIG. 3 illustrates an exemplary frame format of a physical (PHY) frameused in the wireless communication environment according to theembodiment.

FIG. 4 illustrates an exemplary frame format of an acknowledgment (Ack)frame used in the wireless communication environment according to theembodiment.

FIG. 5 illustrates an exemplary hardware configuration of an electronicapparatus according to the embodiment.

FIG. 6 illustrates an exemplary functional configuration of theelectronic apparatus according to the embodiment.

FIG. 7 illustrates an outline of operation of the electronic apparatusaccording to the embodiment.

FIG. 8 is a flowchart illustrating an example of the operation of theelectronic apparatus according to the embodiment.

FIG. 9 is a diagram for illustrating further functions of the electronicapparatus according to the embodiment.

FIG. 10 is another diagram for illustrating further functions of theelectronic apparatus according to the embodiment.

FIG. 11 is a diagram illustrating an outline of another operation of theelectronic apparatus according to the embodiment.

FIG. 12 is another diagram illustrating the outline of the otheroperation of the electronic apparatus according to the embodiment.

FIG. 13 is still another diagram illustrating the outline of the otheroperation of the electronic apparatus according to the embodiment.

DETAILED DESCRIPTION

In general, according to one embodiment, an electronic apparatusincludes a receiver and a transmitter. The receiver is configured toreceive, from a first wireless apparatus, a first physical frameincluding a destination address receivable by a second wirelessapparatus different from the electronic apparatus. The transmitter isconfigured to transmit, to the first wireless apparatus, a firstresponse frame including first information regarding the first physicalframe, if the first physical frame is successfully received. Atransmission period of the first response frame at least partiallyoverlaps with a transmission period of a second response frame, if thefirst physical frame is successfully received by the electronicapparatus and if the first physical frame is successfully received bythe second wireless apparatus, the second response frame includingsecond information regarding the first physical frame received by thesecond wireless apparatus.

Hereinafter, embodiments will be described with reference to theaccompanying drawings. The present disclosure is merely an example, andthe present invention is not limited to the contents described in thefollowing embodiments. Naturally, modifications that can be easilyconceived by those skilled in the art are included in the scope of thepresent disclosure. In order to make the descriptions clearer, there maybe a case where a size, shape, and the like of each part are changedwith respect to actual embodiments and schematically illustrated in thedrawings. In a plurality of the drawings, corresponding elements aredenoted by the same reference numerals, and detailed descriptions may beomitted.

In one exemplary mechanism for achieving highly reliable wirelesscommunication, one wireless terminal transmits one piece of data to aplurality of wireless base stations simultaneously. When data from thewireless terminal is received, each wireless base station sequentiallysends a response frame (Ack frame) back to the wireless terminal in atime-sharing manner. According to this mechanism, since the wirelessterminal transmits one piece of data to a plurality of wireless basestations simultaneously, it becomes possible to refer to the Ack framesfrom the plurality of wireless base stations to determine whether thedata is received by another wireless terminal, whereby wirelesscommunication highly reliable for the wireless terminal can be achieved.

That is, in this mechanism, as the number of wireless base stations tobe destinations of data transmitted from the wireless terminalincreases, the reliability of the wireless communication can beimproved. Meanwhile, as the number of wireless base stations to bedestinations of data transmitted from the wireless terminal increases,the time required for receiving the Ack frame in the wireless terminalalso increases, thereby increasing the overhead accordingly. In view ofthe above, there has been a demand for a new technique capable ofperforming highly reliable wireless communication without increasing theoverhead.

In the present embodiment, the communication frame may also be referredto as a physical frame.

FIG. 1 illustrates a schematic configuration example of a wirelesscommunication system (wireless communication environment) including anelectronic apparatus according to one embodiment. The wirelesscommunication system illustrated in FIG. 1 includes a wireless localarea network (LAN) system including a wireless terminal station (STA)and a first wireless base station AP1 (also referred to as “main accesspoint (AP)”) communicably connected to the wireless terminal STA, and asecond wireless base station AP2 (also referred to as “sub AP”)different from the first wireless base station AP1. Note that theelectronic apparatus according the present embodiment corresponds to thesecond wireless base station AP2. In the present embodiment, it isassumed that the wireless terminal STA is not connected to (associatedwith) the second wireless base station AP2.

Note that, although the wireless LAN system described above is assumedto be a network system in an infrastructure mode including one wirelessbase station AP and at least one wireless terminal STA in the presentembodiment, it is not limited thereto, and may be a network system in anad-hoc mode in which a plurality of wireless terminal STAs directlyperforms communication without interposing a wireless base station AP,for example. However, in this case, any one of the plurality of wirelessterminal STAs is required to operate as an owner in the ad-hoc network.Further, the wireless base station AP included in the wireless LANsystem is not necessarily a wireless base station fixed at apredetermined point. For example, a wireless terminal STA that functionsas a simple wireless base station by changing an operation mode may beregarded as a wireless base station included in the wireless LAN system.

Note that the first and second wireless base stations AP1 and AP2 may beconnected to a controller (not illustrated) via Ethernet (registeredtrademark). As will be described in detail later, this controllerperforms, on the first and second wireless base stations AP1 and AP2,setting of various parameters necessary for highly reliable wirelesscommunication.

Hereinafter, before describing the second wireless base station AP2capable of achieving highly reliable wireless communication for thewireless terminal STA, a frame format used in the wireless communicationsystem illustrated in FIG. 1 will be described in order with referenceto FIGS. 2 to 4.

FIG. 2 illustrates a frame format of a media access control (MAC) frame.As illustrated in FIG. 2, the MAC frame includes a MAC header 11, aframe body 12, and a frame check sequence (FCS) 13.

Information necessary for reception processing in the MAC layer is setin the MAC header 11. Information corresponding to a frame type is setin the frame body 12. An error detection code (cyclic redundancy code(CRC)) calculated to determine whether the MAC header 11 and the framebody 12 have been successfully received in a normal way is set in theFCS 13.

As illustrated in FIG. 2, the MAC header 11 includes a frame controlfield 111, a duration/ID field 112, a plurality of address fields 113 ato 113 d, a sequence control field 114, and a quality of service (QoS)control field 115. Note that the various fields included in the MACheader 11 are not limited to the fields mentioned above, and forexample, a new field may be further added thereto, or some fields may beomitted therefrom.

A value corresponding to the frame type is set in the frame controlfield 111.

More specifically, as illustrated in FIG. 2, the frame control field 111includes a protocol version field 111 a, type field 111 b, sub typefield 111 c, to distribution system (To DS) field 111 d, From DS field111 e, more fragment field 111 f, retry field 111 g, protect field 111h, +HTC/order field 111 i, and the like.

Information indicating a protocol version to be used is set in theprotocol version field 111 a.

Information associated with a type of the MAC frame is set in the typefield 111 b, which indicates whether the type of the MAC frame is amanagement frame, a control frame, or a data frame.

Information indicating the frame type within the frame type indicated bythe type field 111 b is set in the sub type field 111 c.

Information associated with a destination is set in the To DS field 111d, which indicates whether the destination is the wireless base stationAP or the wireless terminal STA. Specifically, it indicates that thedestination is the wireless base station AP when the bit is “1”, andindicates that the destination is the wireless terminal STA when the bitis “0”.

Information associated with a transmission source is set in the From DSfield 111 e, which indicates whether the transmission source is thewireless base station AP or the wireless terminal STA. Specifically, itindicates that the transmission source is the wireless base station APwhen the bit is “1”, and indicates that the transmission source is thewireless terminal STA when the bit is “0”.

The more fragment field 111 f is used when a packet of the upper layeris fragmented and transmitted, and information indicating whether afragment frame subsequently exists is set therein. Specifically, itindicates that a fragment frame subsequently exists when the bit is “1”,and indicates that no fragment frame subsequently exists when the bit is“0”.

Information indicating whether the frame is retransmitted (retransmittedframe) is set in the retry field 111 g. Specifically, it indicates thatthe frame is a retransmitted frame when the bit is “1”, and indicatesthat the frame is not the retransmitted frame when the bit is “0”.

Information indicating whether the frame is encrypted is set in theprotect field 111 h. Specifically, it indicates that the frame isencrypted when the bit is “1”, and indicates that the frame is notencrypted when the bit is “0”.

The +HTC/order field 111 i indicates that the order of frames should notbe changed during frame relay in a case where a non-QoS data frame istransmitted, and indicates that the MAC header includes ahigh-throughput (HT) control field (not illustrated) in a case where aQoS data frame in an IEEE 802.11n/ac/ax physical frame is transmitted.When the HT control field is included, it is included between the QoScontrol field 115 and the frame body 12, and is used to notify a part offunctions defined by IEEE 802.11n/ac/ax.

Note that the various fields included in the frame control field 111 arenot limited to the fields mentioned above, and for example, a new fieldmay be further added thereto, or some fields may be omitted therefrom.

The duration/ID field 112 has a length of 16 bits, and low-order 15 bitsthereof indicate a network allocation vector (NAV) when the mostsignificant bit (MSB) is “0”, and a part of the low-order 15 bitsindicate an identification number allocated to the wireless terminal STAconnected to the wireless base station AP when the MSB is “1”.

A MAC address of a direct receiving station is set in an address 1 field113 a, which is used in determining whether the frame is addressed toits own apparatus, for example. A MAC address of a direct transmittingstation is set in an address 2 field 113 b. In an address 3 field 113 c,the MAC address of the apparatus to be the final destination is set inthe uplink, and the MAC address of the apparatus as the transmissionsource is set in the downlink.

An address 4 field 113 d is set only when the wireless base station APtransmits a frame to another wireless base station AP, and the MACaddress of the apparatus as the transmission source is set therein.

The sequence control field 114 indicates a sequence number of a frame tobe transmitted and a fragment number for a fragment.

The QoS control field 115 is a field added when the frame type indicatedby the type field 111 b is the data frame and the type of the MAC frameindicated by the sub type field 111 c is QoS data. The QoS control field115 includes a traffic ID (TID) field in which an identifiercorresponding to data traffic is set, an Ack policy field in which anacknowledgment method is set, and the like. For example, the TID fieldis used in determining a data traffic type. Further, the Ack policyfield is used in determining whether the QoS data is transmittedaccording to a normal Ack policy, a block Ack policy, or a no Ackpolicy.

FIG. 3 illustrates a frame format of a physical (PHY) frame. Asillustrated in FIG. 3, the PHY frame includes a PHY header 21 and a PHYpayload 22. As further illustrated in FIG. 3, the PHY header 21 includesa non-HT short training field (L-STF) 21 a, a non-HT long training field(L-LTF) 21 b, and a non-HT signal field (L-SIG) 21 c.

The L-STF 21 a and the L-LTF21 b indicate a known bit pattern. Forexample, the receiver that receives the frame refers to the bit patternto perform receiving power adjustment, timing synchronization, channelestimation, and the like. Furthermore, the L-SIG 21 c includesinformation indicating a transmission rate, information indicating aframe length, information regarding a bandwidth, and the like.

The PHY payload 22 includes information indicating a MAC frame havingbeen subject to orthogonal frequency divisional multiplexing (OFDM)modulation processing. That is, the PHY payload 22 is a partcorresponding to the MAC frame illustrated in FIG. 2.

Note that, although the frame format of the PHY frame defined by IEEE802.11a is illustrated in FIG. 3, a frame format of the PHY framedefined by another IEEE 802.11 standard may be used in the wirelesscommunication system illustrated in FIG. 1.

FIG. 4 illustrates a frame format of the Ack frame. The Ack frame is atype of the MAC frame, which includes a frame control field 31, aduration/ID field 32, an address 1 field 33, and an FCS 34, asillustrated in FIG. 4. As the various fields 31 to 34 have already beendescribed, detailed descriptions thereof will be omitted here. Tobriefly supplement the descriptions, in the case of the Ack frame,information indicating the Ack frame is set in the (type field and subtype field of) frame control field 31, and information indicating thedestination of the Ack frame is set in the address 1 field 33.

The various frame formats used in the wireless communication systemillustrated in FIG. 1 have been described above.

Next, a hardware configuration of the second wireless base station AP2illustrated in FIG. 1 will be described with reference to FIG. 5. Asillustrated in FIG. 5, the second wireless base station AP2 includes anantenna 41, a wireless unit 42, an A/D converter 43, a demodulator 44, ahost processor 45, a memory 46, an I/O unit 47, a modulator 48, a D/Aconverter 49, and the like.

The host processor 45 is connected to the memory 46 and the I/O unit 47via a bus. The host processor 45 may implement various functions to bedescribed later by executing a program downloaded from an externalapparatus by the I/O unit 47 and stored in the memory 46 (i.e., bysoftware), may implement the various functions by hardware, or mayimplement the various functions by a combination of software andhardware.

The antenna 41 transmits and receives a wireless signal using, forexample, a frequency in the 2.4 GHz band or the 5 GHz band. The wirelessunit 42 converts the frequency of the wireless signal received by theantenna 41 into a signal in an appropriate frequency band. The A/Dconverter 43 converts the analog signal having been subject to thefrequency conversion using the wireless unit 42 into a digital signal.The demodulator 44 executes, on the digital signal having been subjectto the frequency conversion using the A/D converter 43, receptionprocessing including demodulation and decode conforming to apredetermined standard (e.g., IEEE 802.11a, IEEE 802.11b, IEEE 802.11g,IEEE 802.11n, IEEE 802.11ac, and IEEE 802.11ax, including 802.11standard to be defined in the future) to convert the digital signal intothe MAC frame defined by the predetermined standard. The converted MACframe is transferred to the host processor 45.

The demodulator 44 described above executes, on the digital signalconverted by the A/D converter 43, OFDM symbol timing synchronization,fast Fourier transformation (FFT), deinterleaving, error correctiondecode, and the like as reception processing. The demodulator 44 alsoextracts information (PHY header information) included in the PHY header21 described with reference to FIG. 3. The extracted PHY headerinformation is transferred to the host processor 45. The configurationand its function used at the time of reception processing have beendescribed above.

Next, a configuration and its function used at the time of transmissionprocessing will be described.

The modulator 48 executes, on the MAC frame (e.g., Ack frame)transferred from the host processor 45, transmission processingincluding modulation and encode conforming to a predetermined standardto convert the MAC frame into a digital signal. Note that, as will bedescribed in detail later, the host processor 45 notifies the modulator48 of a PHY parameter to be used at the time of modulation. The D/Aconverter 49 converts the digital signal converted by the modulator 48into an analog signal (baseband signal). The wireless unit 42up-converts the baseband signal converted by the D/A converter 49 to apredetermined frequency band (e.g., 2.4 GHz band and 5 GHz band). Theup-converted signal is transmitted to, as a wireless signal, thewireless terminal STA by the antenna 41.

Next, a functional unit implemented by a program stored in the memory 46being executed by the host processor 45 will be described with referenceto FIG. 6. Note that, although the case where various functional unitsare implemented by software is exemplified here, the various functionalunits may be implemented by hardware, or may be implemented by acombination of software and hardware, as described above.

As illustrated in FIG. 6, the host processor 45 includes an addressmanagement unit 451, a PHY parameter setting unit 452, a frame analyzer453, a response determiner 454, a time measurement unit 455, controller456, and the like.

The address management unit 451 manages the MAC address set in its ownapparatus (own station).

The PHY parameter setting unit 452 generates a PHY parameter necessaryfor transmitting the Ack frame to the wireless terminal STA, andnotifies the modulator 48 of the generated PHY parameter. The PHYparameter is a parameter used at the time when the modulator 48 performsmodulation, which is, specifically, information indicating atransmission rate of the Ack frame, a length of the Ack frame (number ofbytes), a scramble seed (scrambling sequence), and the like. Note thatthe PHY parameter setting unit 452 generates the PHY parameter thatmatches the PHY parameter used in the first wireless base station AP1.In addition, although the PHY parameter includes information indicatinga scramble seed in the present embodiment, it is not limited thereto,and may be any parameter as long as it defines a manner of scramblingfor generating at least part of the PHY frame, for example, the PHYpayload.

Here, a method of generating (determining) the PHY parameter will besupplementarily described.

The transmission rate of the Ack frame indicated by the PHY parameter isdetermined in accordance with the standard of the wireless LAN.Specifically, the transmission rate of the Ack frame is determined to bea value equal to or smaller than the value of the transmission rate atthe time when a received frame is transmitted (i.e., value of thetransmission rate indicated by the PHY header information), and is alsodetermined to be a value of the transmission rate highest among theessential rates. For example, in a case where the standard of thewireless LAN is IEEE 802.11a, there are eight types of availabletransmission rates, that is, 6, 9, 12, 18, 24, 36, 48, 54 [Mbps]. Amongthose eight types of transmission rates, three types of 6, 12, 24 [Mbps]are the transmission rates regarded as the essential rates.

Accordingly, for example, when the value of the transmission rate at thetime when the received frame is transmitted is 24 to 54 [Mbps], 24[Mbps] indicating the highest value among the essential rates of 24[Mbps] or less is determined to be the transmission rate of the Ackframe. Likewise, when the value of the transmission rate at the timewhen the received frame is transmitted is 12 to 18 [Mbps], 12 [Mbps]indicating the highest value among the essential rates of 12 [Mbps] orless is determined to be the transmission rate of the Ack frame.Moreover, when the value of the transmission rate at the time when thereceived frame is transmitted is 6 to 9 [Mbps], 6 [Mbps] indicating thehighest value among the essential rates of 6 [Mbps] or less isdetermined to be the transmission rate of the Ack frame.

The frame length of the Ack frame indicated by the PHY parameter isdetermined in accordance with the standard of the wireless LAN.Specifically, as exemplified in FIG. 4, the frame length of the Ackframe is 2 bytes for the frame control field 31, 2 bytes for theduration/ID field 32, 6 bytes for the address 1 field 33, and 4 bytesfor the FCS 34, which is 14 bytes in total. The frame length of the Ackframe is not limited thereto, and can be defined in accordance with thestandard of wireless communication.

The scramble seed indicated by the PHY parameter is determined to be theone same as the scramble seed inserted in the data frame transmittedfrom the wireless terminal STA (i.e., it is determined to be thescramble seed same as the scramble seed applied at the time when thewireless terminal STA transmits the data frame). Alternatively, thescramble seed is determined in accordance with an instruction from thecontroller mentioned above. Note that, since the PHY parameters need tomatch between the first and second wireless base stations AP1 and AP2 asdescribed above, the instruction from the controller mentioned above istransmitted to the first and second wireless base stations AP1 and AP2in common.

The various functional units will be described again.

The frame analyzer 453 performs analysis based on the MAC frame and thePHY header information transferred from the demodulator 44.

Specifically, the frame analyzer 453 extracts, from the address 1 field113 a included in the MAC frame transferred from the demodulator 44, theMAC address of the receiver that receives the MAC frame. The extractedMAC address is used to determine whether the transferred MAC frame isaddressed to the own station.

Moreover, the frame analyzer 453 refers to the PHY header informationtransferred from the demodulator 44 to determine whether the MAC frametransferred from the demodulator 44 is an aggregate-MAC protocol dataunit (A-MPDU) frame defined by the standard of IEEE 802.11 (e.g., IEEE802.11n). Alternatively, the frame analyzer 453 refers to the (typefield 111 b and sub type field 111 c of) frame control field 111included in the MAC frame transferred from the demodulator 44 todetermine whether the MAC frame is a block Ack request frame thatrequests a block Ack.

Note that, between the two methods of determination described above, theformer one is a method of indirectly determining whether the MAC frameis the block Ack request frame, and the latter one is a method ofdirectly determining whether the MAC frame is the block Ack requestframe.

Further, the frame analyzer 453 refers to the (type field 111 b of)frame control field 111 included in the MAC frame transferred from thedemodulator 44 to determine whether the MAC frame is a data frame.Furthermore, the frame analyzer 453 calculates a checksum based on theMAC frame transferred from the demodulator 44 to determine whether thecalculated checksum and the checksum set (specified) in the MAC frameare identical (i.e., it is determined whether the MAC header 11 and theframe body 12 have been successfully received).

The response determiner 454 determines whether the wireless signaltransmitted from the wireless terminal STA (i.e., MAC frame transferredfrom the demodulator 44) has been transmitted to the own station.Specifically, the response determiner 454 compares the MAC address ofthe own station, which is managed by the address management unit 451,with the MAC address extracted by the frame analyzer 453 to determinewhether the two MAC addresses match, thereby determining whether it istransmitted to the own station.

When it is determined that the Ack frame should be returned to thewireless terminal STA, the time measurement unit 455 measures theelapsed time from the end of the received frame (i.e., MAC frametransferred from the demodulator 44), and when the period of timereferred to as short inter-frame spacing (SIFS) has elapsed, notifiesthe host processor 45 of the status. The SIFS indicates the shortestlatency time until the Ack frame is returned, which is, for example, 16[ρsec]. Upon reception of the notification, the host processor 45notifies the modulator 48 of an instruction to transmit the Ack frame.

The controller 456 controls the various functional units 451 to 455described above.

Next, exemplary operation executed by the second wireless base stationAP2 having the configuration illustrated in FIGS. 5 and 6 to achievehighly reliable wireless communication for the wireless terminal STAwill be described. Note that the exemplary operation of the secondwireless base station AP2 in the case where the wireless terminal STAtransmits the wireless signal (in this case, data frame) addressed tothe first wireless base station AP1 in the wireless communicationenvironment illustrated in FIG. 1 will be described here.

When the wireless terminal STA transmits the data frame addressed to thefirst wireless base station AP1, normally, only the first wireless basestation AP1 returns the Ack frame to the wireless terminal STA. However,as schematically illustrated in FIG. 7, in the case where the dataframe, which is originally addressed to another station, is recognizedas the data frame addressed to the own station, the second wireless basestation AP2 according to the present embodiment executes the operationof returning the Ack frame to the wireless terminal STA after the periodof time referred to as SIFS has elapsed from the end of the data frame.

The transmission timing of the Ack frame by the second wireless basestation AP2 is preferably controlled not to exceed the guard intervaltime of the Ack frame (e.g., 0.8 μsec according to the standard of IEEE802.11a, and predetermined time length defined by another standard) withrespect to the transmission timing of the Ack frame by the firstwireless base station AP1 (i.e., in the example of the standard of IEEE802.11a, the timing is preferably controlled such that the difference is0.8 μsec or less when it is transmitted earlier than the Ack frametransmitted by the first wireless base station AP1 and the difference is0.8 μsec or less when it is transmitted later). Accordingly, the periodof time in which the Ack frame is transmitted by the first wireless basestation AP1 and the period of time in which the Ack frame is transmittedby the second wireless base station AP2 at least partly overlap eachother.

The guard interval indicates time for creating an interval betweenconsecutive OFDM symbols in the physical frame, which is a mechanism formaking the preceding and following OFDM symbol signals less likely tooverlap each other due to the influence of multipath or the like.

FIG. 8 is a flowchart for illustrating the operation of the secondwireless base station AP2 schematically illustrated in FIG. 7 in moredetail.

First, the second wireless base station AP2 receives the wireless signaladdressed to the first wireless base station AP1 via the antenna 41.Thereafter, the second wireless base station AP2 converts the receivedwireless signal into a MAC frame using the wireless unit 42, the A/Dconverter 43, and the demodulator 44, and transfers it to the hostprocessor 45. At this time, the demodulator 44 extracts the PHY headerinformation included in the PHY header 21 of the received frame, andalso transfers the extracted PHY header information to the hostprocessor 45.

As a result, the host processor 45 of the second wireless base stationAP2 receives the MAC frame addressed to the first wireless base stationAP1, and also receives the input of the PHY header information extractedby the demodulator 44 (block B1).

Next, the frame analyzer 453, which is a functional unit of the hostprocessor 45, determines whether the received MAC frame is a block Ackrequest frame (i.e., the frame analyzer 453 determines whether thereceived MAC frame includes a plurality of data frames) (block B2). Asdescribed above, the method of determining whether the MAC frame is theblock Ack request frame may be an indirect method of determining whetherthe MAC frame is an A-MPDU frame by referring to the PHY headerinformation transferred from the demodulator 44, or may be a directmethod of determination by referring to the frame control field 111 ofthe MAC frame.

If it is determined that the received MAC frame is a block Ack requestframe (YES in block B2), the host processor 45 determines not to returnthe Ack frame to the wireless terminal STA, discards the received MACframe (block B3), and terminates the series of operations here.

On the other hand, if it is determined that the received MAC frame isnot a block Ack request frame (NO in block B2), the frame analyzer 453refers to the frame control field 111 of the received MAC frame todetermine whether the MAC frame is a data frame (block B4). If it isdetermined that the received MAC frame is not a data frame (NO in blockB4), the host processor 45 executes the processing of block B3 describedabove, and terminates the series of operations here.

If it is determined that the received MAC frame is a (single) data frame(YES in block B4), the frame analyzer 453 extracts the MAC address setin the address 1 field 113 a of the received MAC frame (block B5). Theextracted MAC address is transferred to the response determiner 454.

The response determiner 454 compares the MAC address transferred fromthe frame analyzer 453 with the MAC address of the own station managedby the address management unit 451 to determine whether those two MACaddresses match (block B6). If it is determined that the two MACaddresses do not match (NO in block B6), the host processor 45 executesthe processing of block B3 described above, and terminates the series ofoperations here.

On the other hand, if it is determined that the two MAC addresses match(YES in block B6), the response determiner 454 notifies the frameanalyzer 453 of the determination result. Upon reception of thenotification from the response determiner 454, the frame analyzer 453calculates a checksum based on the received MAC frame to determinewhether the calculated checksum and the checksum set in the MAC framematch (block B7). If it is determined that the checksums do not match(NO in block B7), the host processor 45 executes the processing of blockB3 described above, and terminates the series of operations here.

If it is determined that the checksums match (i.e., the MAC frame issuccessfully received) (YES in block B7), the (response determiner 454of) host processor 45 determines to return the Ack frame to the wirelessterminal STA, generates the Ack frame, and notifies the PHY parametersetting unit 452 and the time measurement unit 455 of the status (blockB8). Upon reception of the notification, the time measurement unit 455starts to measure the elapsed time from the end of the received MACframe.

Subsequently, upon reception of the notification that the Ack frame isdetermined to be returned to the wireless terminal STA, the PHYparameter setting unit 452 generates the PHY parameter necessary formodulation processing for returning the Ack frame, and transfers it tothe modulator 48 (block B9).

Thereafter, upon reception of the notification from the time measurementunit 455 that the period of time referred to as SIFS has elapsed, thehost processor 45 notifies the modulator 48 of an instruction fortransmitting the Ack frame, transfers the generated Ack frame (blockB10), and terminates the series of operation here. As a result, the Ackframe is returned from the second wireless base station AP2 to thewireless terminal STA.

The wireless terminal STA calculates a checksum of each Ack framereturned from the first and second wireless base stations AP1 and AP2,and when each checksum matches the checksum set in each Ack frame, it isdetermined that the Ack frame has been successfully received in a normalmanner.

Alternatively, the wireless terminal STA may determine that the Ackframe has been received when a certain wireless signal is detected afterthe SIFS has elapsed from the end of the transmitted data frame (whenclear channel assessment (CCA) is determined to be in a busy state). Itshould be noted that the period of the busy state is equal to or longerthan the length of the PHY preamble (e.g., 8 μsec) or the length of thePHY header (e.g., 20 μsec), and is equal to or shorter than the maximumtransmission time of the Ack frame (e.g., 44 μsec), with the time pointat which the SIFS has elapsed from the end of the transmitted data frameserving as a starting point.

Alternatively, the wireless terminal STA may check up to the PHY headerof the frame being transmitted, and may determine that the Ack frame hasbeen received when the frame length indicated by the PHY header is setto 14.

Furthermore, the wireless terminal STA may check the type field and thesub type field of the frame control field 31 included in the MAC framebeing transmitted, and may determine that the Ack frame has beenreceived when information indicating the Ack frame is set therein.Alternatively, the wireless terminal STA may check the address 1 field33 included in the MAC frame being transmitted, and may determine thatthe Ack frame has been received when information indicating the MACaddress of its own apparatus is set therein.

Note that, although several methods by which the wireless terminal STAdetermines that the Ack frame has been received have been describedhere, the methods described above may be used in optional combination.

In addition, as long as at least one of the Ack frames returned from thefirst and second wireless base stations AP1 and AP2 has beensuccessfully received in a normal manner, even if the Ack frame from theother one has not been successfully received in a normal manner, thewireless terminal STA transmits a new next data frame withoutretransmitting the data frame having already been transmitted.

According to the series of operations described above, the secondwireless base station AP2 can return the Ack frame to the data frameaddressed to another station, whereby highly reliable wirelesscommunication for the wireless terminal STA can be achieved. Moreover,since the wireless terminal STA does not transmit the data frame to thesecond wireless base station AP2, it is not necessary to sequentiallyreceive the Ack frames from the first and second wireless base stationsAP1 and AP2 in a time-sharing manner as in the conventional systemdescribed above, whereby an increase in overhead can be suppressed.

Note that, in order for the second wireless base station AP2 to returnthe Ack frame to the data frame addressed to the other station, asdescribed in the block B6 described above, the MAC address set in theaddress 1 field 113 a of the received MAC frame needs to match the MACaddress managed by the address management unit 451. That is, the secondwireless base station AP2 needs to recognize that the data frameaddressed to the other station is a data frame addressed to its ownstation. Accordingly, in the present embodiment, the MAC address of thesecond wireless base station AP2 is set according to one of thefollowing methods.

There is a first exemplary method of setting the MAC address of thesecond wireless base station AP2 to the MAC address same as the uniqueMAC address of the first wireless base station AP1. Note that the MACaddress of the first wireless base station AP1 may be obtained from thefirst wireless base station AP1, and may be obtained via the controllerdescribed above.

According to this first setting method, the MAC address managed by theaddress management unit 451 is the same as the MAC address of the firstwireless base station AP1, whereby the second wireless base station AP2can recognize all data frames transmitted from the wireless terminal STAto the first wireless base station AP1, which is the other station, asdata frames addressed to its own station.

There is a second exemplary method of setting two MAC addresses in thesecond wireless base station AP2. More specifically, there is a methodby which a unique MAC address different from the unique MAC address ofthe first wireless base station AP1 is set as a first address and a MACaddress common to the first wireless base station AP1, which isdifferent from the unique MAC address of the first wireless base stationAP1, is additionally set as a second address. That is, two MAC addressesare set in both of the first and second wireless base stations AP1 andAP2, respectively, and one of them is set to be a common MAC address.

Examples of a method of setting, as a second address, a common MACaddress in the first and second wireless base stations AP1 and AP2include a method using a local address. That is, a MAC address thatfunctions as a global address is set as a first address, and a MACaddress that functions as a local address is set as a second address.Specifically, the MAC address in which other fields are set in anappropriate byte sequence in the state where the global/local (G/L) bitis set to “1” is generated as a second address, which is set in thefirst and second wireless base stations AP1 and AP2. Note that thesecond address is generated by the controller described above, forexample, and the first and second wireless base stations AP1 and AP2 arenotified of the second address and set the second address.

According to this second setting method, the wireless terminal STA canachieve highly reliable wireless communication selectively in such amanner that the second address notified by the first wireless basestation AP1 is used as a destination only when the highly reliablewireless communication is desired while the first address notified bythe first wireless base station AP1 is used as a destination when thehighly reliable wireless communication is not required. That is, thesecond wireless base station AP2 can recognize, instead of recognizingthat all data frames transmitted from the wireless terminal STA to thefirst wireless base station AP1 are data frames addressed to its ownstation, that the data frame transmitted to the first wireless basestation AP1 is the data frame addressed to its own station as necessary.

There is a third exemplary method of setting the MAC address of thesecond wireless base station AP2 to be serial-numbered with the uniqueMAC address of the first wireless base station AP1 (i.e., there is thethird exemplary method of setting the MAC address of the second basestation AP2 to be different from an address of the first wireless basestation AP1 by a value of at least one bit). In this method, the addressmanagement unit 451 of the second wireless base station AP2 manages maskbits capable of specifying bits not to be compared in the processing ofthe block B6 described above together with the MAC address.

This method will be concretely described. For example, in the case wherethe MAC address of the first wireless base station AP1 is“AB:CD:E0:00:12:34”, the MAC address of the second wireless base stationAP2 is set to “AB:CD:E0:01:12:34”. At this time, the address managementunit 451 manages “00:00:00:01:00:00” as a mask bit. The mask bitindicates that the MAC address of the bit position where “1” is set isnot compared (treated as “Don't care”). Accordingly, the MAC address“AB:CD:E0:00:12:34” of the first wireless base station AP1 and the MACaddress “AB:CD:E0:01:12:34” of the second wireless base station AP2 aresubstantially the same in the processing of the block B6 describedabove, whereby the second wireless base station AP2 can recognize thedata frame addressed to the first wireless base station AP1, which isthe other station, as a data frame addressed to its own station. Notethat, although the exemplary case where the serial number included inthe MAC address is masked by the mask bit has been described here, it isnot limited thereto, and an arbitrary bit may be masked by the mask bit.

According to this third setting method, the effect similar to that inthe case of the first setting method described above can be obtained.Further, by dynamically changing the mask bit (e.g., “00:00:00:01:00:00”is set at one point in time and “00:00:00:00:00:00” is set at anotherpoint in time), the effect similar to that in the case of the secondsetting method can be obtained.

Note that, although the data frame addressed to the other stationindicates the data frame addressed to the first wireless base stationAP1 different from the own station from the viewpoint of the secondwireless base station AP2 in the present embodiment, it is not limitedthereto, and for example, a data frame addressed to a MAC addressdifferent from the first address in the second method described above(e.g., second address) may be referred to as a data frame addressed tothe other station. Furthermore, a data frame transmitted to a wirelessbase station (in this case, first wireless base station AP1) to whichthe wireless terminal STA is connected (associated) may be referred toas a data frame addressed to the other station.

In order to cause a plurality of wireless base stations to receive thedata frame transmitted by the wireless terminal STA, a method ofsetting, to the first address of the data frame, a group address such asbroadcast is available. However, it is preferable to set a unicastaddress in the first address. The reason is that, for example, in thecase where the first address of the data frame is a group address, awireless apparatus that does not need to receive the data frame alsoreceives the data frame so that excess operation power is wasted, andthat an additional mechanism for the wireless base station to transmit aresponse frame to a broadcast data frame is not necessary in the case ofa unicast data frame. Meanwhile, the method of setting, to the firstaddress of the data frame, a group address such as broadcast hasadvantages such as ease of implementation.

Moreover, although the PHY parameter is the information indicating thetransmission rate of the Ack frame, the frame length of the Ack frame,and the scramble seed in the present embodiment, it is not limitedthereto, and the PHY parameter may further indicate the followinginformation.

For example, in the case where the first and second wireless basestations AP1 and AP2 have multiple antennas (multiple-input andmultiple-output (MIMO) function), the PHY parameter may further indicatethe number of streams and the number of antennas. In general, in thecase where the wireless base station AP has the MIMO function andtransmission in which the number of antennas is larger than the numberof streams of the transmission frame (Ack frame) is performed,performing cyclic shift is defined by the standard of IEEE 802.11.Accordingly, occurrence of unintended directivity can be avoided.However, when the cyclic shift is performed, the multipath is recognizedto be lengthened on the side of the wireless terminal STA, whereby thereis a possibility that the multipath exceeds the guard interval.Accordingly, there is a possibility that the wireless terminal STAerroneously recognize that interference is occurring. Therefore, bymatching the number of streams and the number of antennas using the PHYparameter, occurrence of the situation mentioned above can besuppressed.

Alternatively, the PHY parameter may further indicate a deviation of thecenter frequency from the wireless terminal STA. In general, even whenthe wireless base station AP and the wireless terminal STA use the samefrequency channel, a deviation of the center frequency occurs notinfrequently. Therefore, by analyzing the deviation of the centerfrequency to set it as the PHY parameter, at the time when the Ack frameis returned to the wireless terminal STA, the first and second wirelessbase stations AP1 and AP2 can return the Ack frame after correcting thedeviation of the center frequency.

In addition to the functions described above, as exemplified in FIG. 9,the second wireless base station AP2 may have a function of determining,when a retransmitted frame addressed to the other station isconsecutively received from the wireless terminal STA a predeterminednumber of times, that the Ack frame transmitted by its own may have anadverse effect and stopping returning the Ack frame to the retransmittedframe. Note that the second wireless base station AP2 can determine, byreferring to the retry field 111 g of the frame control field 111included in the data frame addressed to the other station, whether thedata frame is a retransmitted frame. Alternatively, the second wirelessbase station AP2 may refer to the sequence control field 114 included inthe data frame addressed to the other station to determine whether theframe having the same sequence number has been received a predeterminednumber of times or more, thereby determining whether the data frame is aretransmitted frame. Further, the second wireless base station AP2 mayrefer to the retry field 111 g of the frame control field 111 and thesequence control field 114 included in the data frame addressed to theother station to determine whether the retry field 111 g indicates “1”and the frame having the same sequence number has been received apredetermined number of times or more, thereby determining whether thedata frame is a retransmitted frame.

Furthermore, as illustrated in FIG. 10, the second wireless base stationAP2 may further have a function of, by recognizing beforehand the MACaddress of the wireless terminal STA incapable of achieving highlyreliable wireless communication even when the Ack frame is returned, notreturning the Ack frame to the data frame transmitted from the wirelessterminal STA. For example, the MAC address of the wireless terminal STAincapable of achieving highly reliable wireless communication may be setin advance in the second wireless base station AP2 by the controller.Alternatively, the second wireless base station AP2 may generate a listof the MAC addresses of the wireless terminal STAs incapable ofachieving highly reliable wireless communication from informationassociated with a past wireless communication history (e.g., informationindicating that the repetition at which the wireless terminal STAretransmits the data frame exceeds a predetermined number of times evenwhen the second wireless base station AP2 returns the Ack frame). Notethat the second wireless base station AP2 refers to the address 2 field113 b included in the data frame addressed to the other station so thatthe MAC address of the wireless terminal STA that has transmitted thedata frame can be grasped, whereby the second wireless base station AP2can determine whether the wireless terminal STA is a wireless terminalSTA incapable of achieving highly reliable wireless communication.

Although the case where the second wireless base station AP2 recognizesthe data frame transmitted from the wireless terminal STA to the firstwireless base station AP1, which is the other station, as a data frameaddressed to its own station and returns the Ack frame has beendescribed in the present embodiment, the second wireless base stationAP2 may recognize a request to send (RTS) frame transmitted from thewireless terminal STA to the first wireless base station AP1, which isthe other station, as an RTS frame addressed to its own station andreturns a clear to send (CTS) frame, as exemplified in FIG. 11. Notethat both the RTS frame and the CTS frame are frames for reserving acommunication period for transmitting the next data frame.

Furthermore, although the case where the second wireless base stationAP2 recognizes the data frame transmitted from the wireless terminal STAto the first wireless base station AP1, which is the other station, as adata frame addressed to its own station and returns the Ack frame hasbeen described in the present embodiment, the second wireless basestation AP2 may recognize a trigger frame and an A-MPDU frametransmitted from the wireless terminal STA to the first wireless basestation AP1, which is the other station, as a frame addressed to its ownstation and returns a block Ack frame, as exemplified in FIG. 12. Theblock Ack frame is a response frame including information regardingacknowledgment of transmission to at least one of a plurality of dataframes included in the A-MPDU frame. In this case, as illustrated inFIG. 12, the second wireless base station AP2 uses a frequency positiondifferent from the frequency position instructed by the trigger frame(i.e., using a frequency different from that of the first wireless basestation AP1) to return the block Ack frame to the wireless terminal STA.Note that the PHY headers of the block Ack frames returned from thefirst and second wireless base stations AP1 and AP2 are the same. Thetrigger frame is a frame for instructing a frequency used fortransmitting the block Ack frame as described above.

In the situation where the wireless terminal STA recognizes theexistence of the second wireless base station AP2 beforehand, thewireless terminal STA may instruct, using the trigger frame, a frequencyposition used by the first wireless base station AP1 and a frequencyposition used by the second wireless base station AP2, respectively. Inthis case, the first and second wireless base stations AP1 and AP2 usethe frequency position instructed by the trigger frame to return theblock Ack frame to the wireless terminal STA.

Note that, in the case where the controller described above notifies thefirst and second wireless base stations AP1 and AP2 of the frequency tobe used for transmitting the block Ack frame beforehand, the wirelessterminal STA may not transmit the trigger frame, as illustrated in FIG.13.

According to the embodiment described above, it is possible to achievehighly reliable wireless communication while an increase in overhead issuppressed.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

What is claimed is:
 1. An electronic apparatus comprising: a receiverconfigured to receive, from a first wireless apparatus, a first physicalframe including a destination address receivable by a second wirelessapparatus different from the electronic apparatus; and a transmitterconfigured to transmit, to the first wireless apparatus, a firstresponse frame including first information regarding the first physicalframe, if the first physical frame is successfully received, wherein atransmission period of the first response frame at least partiallyoverlaps with a transmission period of a second response frame, if thefirst physical frame is successfully received by the electronicapparatus and if the first physical frame is successfully received bythe second wireless apparatus, the second response frame includingsecond information regarding the first physical frame received by thesecond wireless apparatus.
 2. The electronic apparatus of claim 1,wherein the first physical frame includes a first data frame, and thefirst response frame is a first acknowledgment frame includinginformation regarding acknowledgment of the first data frame.
 3. Theelectronic apparatus of claim 2, wherein the receiver is configured toreceive, if the first acknowledgment frame is successfully received bythe first wireless apparatus and a second acknowledgment frame is failedto receive by the first wireless apparatus, a next data frame differentfrom the first data frame without receiving the first data frame again,the second acknowledgment frame including information regardingacknowledgment of the first data from the second wireless apparatus. 4.The electronic apparatus of claim 1, wherein the first physical frameincludes a first request to send (RTS) frame for reserving acommunication period, and the first response frame is a first clear tosend (CTS) frame for reserving the communication period, the CTS frameincluding information regarding the first RTS frame.
 5. The electronicapparatus of claim 4, wherein the receiver is configured to receive, ifthe first CTS frame is successfully received by the first wirelessapparatus and a second CTS frame is failed to receive by the firstwireless apparatus, a transmission data frame during the communicationperiod without receiving the first RTS frame again, the second CTS frameincluding information regarding the first RTS frame from the secondwireless apparatus.
 6. The electronic apparatus of claim 1, wherein atransmission rate of the first and second response frames is the same,and the transmission rate of the first and second response frames isdetermined according to a transmission rate of the first physical framein conformity with a first wireless communication standard to which thesecond wireless apparatus conforms.
 7. The electronic apparatus of claim1, wherein a sequence used for scrambling at least part of physicalframes of the first and second response frames is the same.
 8. Theelectronic apparatus of claim 1, wherein the first physical frameincludes a first data frame and a second data frame, the first responseframe is a first acknowledgment including information regardingacknowledgment of at least one of the first and second data frames, andthe first acknowledgment frame includes a physical header same as aphysical header of a second acknowledgment frame including informationregarding acknowledgment of at least one of the first and second dataframes from the second wireless apparatus.
 9. The electronic apparatusof claim 8, wherein the first acknowledgment frame is transmitted to thefirst wireless apparatus using a first frequency different from a secondfrequency used if the second acknowledgment frame is transmitted by thesecond wireless apparatus.
 10. The electronic apparatus of claim 1,wherein an address of the electronic apparatus is the same as an addressof the second wireless apparatus.
 11. The electronic apparatus of claim10, wherein a global address of the electronic apparatus is differentfrom a global address of the second wireless apparatus, and a localaddress of the electronic apparatus is the same as a local address ofthe second wireless apparatus.
 12. The electronic apparatus of claim 1,wherein an address of the electronic apparatus is different from anaddress of the second wireless apparatus by a value of at least one bit.13. The electronic apparatus of claim 1, wherein the first responseframe is transmitted to the first wireless apparatus if the firstphysical frame includes a data frame, the first response frame includinginformation regarding acknowledgment of the data frame, and the firstresponse frame is not transmitted to the first wireless apparatus if thefirst physical frame includes a plurality of data frames.
 14. Theelectronic apparatus of claim 1, wherein the first response frame is nottransmitted to the first wireless apparatus if the first physical frameis received a predetermined number of times or more.
 15. The electronicapparatus of claim 1, wherein the second wireless apparatus is connectedto the first wireless apparatus, and the electronic apparatus is notconnected to the first wireless apparatus.
 16. An electronic apparatuscomprising: a transmitter configured to transmit a first physical frameincluding a destination address receivable by a first wirelessapparatus; and a receiver configured to receive a response frameincluding information regarding the first physical frame if the firstphysical frame is successfully received by the first wireless apparatus,wherein the receiver is configured to determine that the response framehas been received if a first wireless signal is detected after a lapseof a first period from an end of the first physical frame.
 17. Theelectronic apparatus of claim 16, wherein the receiver is configured todetermine that the response frame has been received if a length of aframe obtained by executing reception processing on the first wirelesssignal is a first value.
 18. The electronic apparatus of claim 16,wherein the receiver is configured to determine that the response framehas been received if a type of the frame obtained by executing receptionprocessing on the first wireless signal indicates the response frame.19. The electronic apparatus of claim 16, wherein the receiver isconfigured to determine that the response frame has been received if adestination of the frame obtained by executing reception processing onthe first wireless signal is the own apparatus.